A PHYSICS 218 EXAM 2 Thursday, October 20, 2011 NAME: ENCIRCLE YOUR SECTION NUMBER: 513 514 515 516 Note: 513 Recitation & lab Wed 8:00-10:50 am 514 Recitation & lab Wed 10:20 am - 1:10 pm 515 Recitation & lab Wed 12:40-3:30 pm 516 Recitation & lab Wed 3:00-5:50 pm There are a total of 7 problems on this test: Problems 1, 2, and 3 are worth 6 or 7 points each. For these three problems, points will be deducted for the wrong units or wrong number of significant digits. Other than that, no partial credit will be awarded for incorrect answers. Problems 4, 5, 6, and 7 are worth 20 points each. For these four problems, partial credit will be awarded where appropriate. For all 7 problems: You must show your work and/or explain your reasoning to receive any credit for a problem; merely stating the answer is NOT sufficient. Write your final answer(s) in the blanks provided. You may use the backs of the pages for scratch calculations if you wish, but only the work in the spaces provided on the front of the pages will be graded. For numerical values, assume that all specified digits are significant, including trailing zeros. Also remember, an answer CAN NOT be completely correct if it has the wrong units or the wrong number of significant digits. G O O D L U C K!!!!!
For problems 1, 2, and 3, do your work in the space provided, and write your final answer in the blank. Points will be deducted for the wrong units or wrong number of significant digits. Other than that, no partial credit will be awarded for incorrect answers. 1. (6 points) In the figure below, a small 4.00 kg block is attached to a vertical post by two massless strings. The entire system is spinning fast enough that both strings are taught. In the blank space to the right of the figure, draw a free body diagram for the block that an Engineering professor would consider acceptable. A 2. (7 points) At a waterpark, sleds with riders are sent along a slippery, horizontal surface by the release of a large compressed spring. The spring with force constant k = 45.0 N/cm and negligible mass rests on the frictionless horizontal surface. One end is in contact with a stationary wall. A sled and rider with total mass 65.0 kg are pushed against the other end, compressing the spring 0.375 m. The sled is then released with zero initial velocity. What is the sled s speed when the spring is still compressed 0.200 m? Speed 3. (7 points) In the figure below, a 0.500 kg block, attached to a spring with length 0.750 m and force constant 40.0 N/m, is initially at rest on a horizontal, frictionless air table. The mass of the spring is negligible. You move the block to the right by pulling with a constant 20.0 N horizontal force. What is the block s speed when you have pulled it 0.330 m from its initial location? Speed
For problems 4, 5, 6, and 7, do your work in the space provided, and write your final answer in the blank. For these problems, partial credit will be awarded where appropriate, based on the work that you show. A 4. (20 points) A pump is required to lift 700. kg of water per minute from a well that is 13.0 m deep and eject it with a speed of 17.0 m/s. (a) How much work is done per minute in lifting the water? (b) How much work is done per minute in giving the water the kinetic energy it has when ejected? (c) What must be the power output of the pump? Work (a) Work (b) Power
5. (20 points) An object of mass 45.0 kg is initially at rest in the middle of the horizontal, frictionless surface of an ice-covered lake. Then a force directed east and with magnitude F(t) = (15.8 N/s)t is applied. (a) How far does the object travel in the first 5.00 s after the force is applied? (b) What is the average power delivered to the object by the force during the first 5.00 s? (c) What is the instantaneous power delivered to the object by the force at t = 5.00 s? Distance Average power Instantaneous power A
6. (20 points) A small rock with mass 0.110 kg is fastened to a massless string with length 0.750 m to form a pendulum. The pendulum is swinging so as to make a maximum angle of 33.0 0 with the vertical. Air resistance is negligible. (a) What is the speed of the rock when the string passes through the vertical position? (b) What is the tension in the string when it makes an angle of 33.0 0 with the vertical? (c) What is the tension in the string as it passes through the vertical? Speed Tension (b) Tension (c) A
7. (20 points) Blocks A, B, and C are placed as shown in the figure below and connected by ropes of negligible mass. Block A weighs 30.0 N. Block B weighs 20.0 N. The coefficient of kinetic friction between block A and the horizontal surface is 0.310; that between block B and the incline plane is 0.260. Block C descends with constant velocity. (a) In the spaces provided below, draw free-body diagrams for blocks A and B that an Engineering professor would find acceptable. (b) What is the tension in the rope connecting blocks A and B? (c) What is the weight of block C? (d) If the rope connecting A and B were cut, what would be the acceleration of block C? Tension Weight Acceleration Block A Block B A
B PHYSICS 218 EXAM 2 Thursday, October 20, 2011 NAME: ENCIRCLE YOUR SECTION NUMBER: 513 514 515 516 Note: 513 Recitation & lab Wed 8:00-10:50 am 514 Recitation & lab Wed 10:20 am - 1:10 pm 515 Recitation & lab Wed 12:40-3:30 pm 516 Recitation & lab Wed 3:00-5:50 pm There are a total of 7 problems on this test: Problems 1, 2, and 3 are worth 5 points each. For these three problems, points will be deducted for the wrong units or wrong number of significant digits. Other than that, no partial credit will be awarded for incorrect answers. Problems 4, 5, 6, and 7 are worth 15 points each. For these four problems, partial credit will be awarded where appropriate. For all 7 problems: You must show your work and/or explain your reasoning to receive any credit for a problem; merely stating the answer is NOT sufficient. Write your final answer(s) in the blanks provided. You may use the backs of the pages for scratch calculations if you wish, but only the work in the spaces provided on the front of the pages will be graded. For numerical values, assume that all specified digits are significant, including trailing zeros. Also remember, an answer CAN NOT be completely correct if it has the wrong units or the wrong number of significant digits. G O O D L U C K!!!!!
For problems 1, 2, and 3, do your work in the space provided, and write your final answer in the blank. Points will be deducted for the wrong units or wrong number of significant digits. Other than that, no partial credit will be awarded for incorrect answers. 1. (6 points) In the figure below, a small 4.00 kg block is attached to a vertical post by two massless strings. The entire system is spinning fast enough that both strings are taught. In the blank space to the right of the figure, draw a free body diagram for the block that an Engineering professor would consider acceptable. B 2. (7 points) At a waterpark, sleds with riders are sent along a slippery, horizontal surface by the release of a large compressed spring. The spring with force constant k = 55.0 N/cm and negligible mass rests on the frictionless horizontal surface. One end is in contact with a stationary wall. A sled and rider with total mass 65.0 kg are pushed against the other end, compressing the spring 0.375 m. The sled is then released with zero initial velocity. What is the sled s speed when the spring is still compressed 0.200 m? Speed 3. (7 points) In the figure below, a 0.500 kg block, attached to a spring with length 0.750 m and force constant 40.0 N/m, is initially at rest on a horizontal, frictionless air table. The mass of the spring is negligible. You move the block to the right by pulling with a constant 20.0 N horizontal force. What is the block s speed when you have pulled it 0.470 m from its initial location? Speed
For problems 4, 5, 6, and 7, do your work in the space provided, and write your final answer in the blank. For these problems, partial credit will be awarded where appropriate, based on the work that you show. B 4. (20 points) A pump is required to lift 700. kg of water per minute from a well that is 12.0 m deep and eject it with a speed of 19.0 m/s. (a) How much work is done per minute in lifting the water? (b) How much work is done per minute in giving the water the kinetic energy it has when ejected? (c) What must be the power output of the pump? Work (a) Work (b) Power
5. (20 points) An object of mass 45.0 kg is initially at rest in the middle of the horizontal, frictionless surface of an ice-covered lake. Then a force directed east and with magnitude F(t) = (16.3 N/s)t is applied. (a) How far does the object travel in the first 5.00 s after the force is applied? (b) What is the average power delivered to the object by the force during the first 5.00 s? (c) What is the instantaneous power delivered to the object by the force at t = 5.00 s? Distance Average power Instantaneous power B
6. (20 points) A small rock with mass 0.140 kg is fastened to a massless string with length 0.750 m to form a pendulum. The pendulum is swinging so as to make a maximum angle of 37.0 0 with the vertical. Air resistance is negligible. (a) What is the speed of the rock when the string passes through the vertical position? (b) What is the tension in the string when it makes an angle of 37.0 0 with the vertical? (c) What is the tension in the string as it passes through the vertical? Speed Tension (b) Tension (c) B
7. (20 points) Blocks A, B, and C are placed as shown in the figure below and connected by ropes of negligible mass. Block A weighs 30.0 N. Block B weighs 20.0 N. The coefficient of kinetic friction between block A and the horizontal surface is 0.350; that between block B and the incline plane is 0.290. Block C descends with constant velocity. (a) In the spaces provided below, draw free-body diagrams for blocks A and B that an Engineering professor would find acceptable. (b) What is the tension in the rope connecting blocks A and B? (c) What is the weight of block C? (d) If the rope connecting A and B were cut, what would be the acceleration of block C? Tension Weight Acceleration Block A Block B B